By not advertising SMTPUTF8 support at the start, senders may opt to transmit recipient internationalized domain names in IDNA form instead, which will be deliverable.
Incoming mail with internationalized domains was probably working prior to our move to Ubuntu 18.04 when postfix's SMTPUTF8 support became enabled by default.
The previous commit is retained because Mail-in-a-Box users might prefer to keep SMTPUTF8 on for outbound mail, if they are not using internationalized domains for email, in which case the previous commit fixes the 'relay access denied' error even if the emails aren't deliverable.
113b7bd827